1. Field of the Invention
The present invention relates to coinjection stretch-blow molded containers with greatly improved impact delamination resistance, good gas barrier properties against oxygen, carbon dioxide, and other gasses, and good appearance, and which may be used as containers for beverages, foods, cosmetics, etc.
2. Description of the Related Art
Thermoplastic polyester (PES) containers produced by a stretch-blow molding process have various excellent properties including good transparency, good mechanical characteristics and good flavor barrier properties, and are sanitary and safe for daily use because they release few residual monomers and other harmful additives. Therefore, they have many applications in various fields. However, since their gas barrier properties are not always satisfactory, drinks, foods and other types of contents filled in such containers could be stored for only a relatively short period of time.
In order to overcome this drawback, various methods of combining a thermoplastic polyester with an ethylene-vinyl alcohol copolymer (EVOH), which has good gas barrier properties, to give laminated structures, have heretofore been proposed. Prior to stretch-blowing, a preform is first formed. Methods of forming the preform include, for example, coinjection molding, coextrusion molding, multi-stage injection molding, etc. Of these methods, coinjection molding may be carried out with a relatively simple apparatus which produces relatively little scrap. The moldings produced by a coinjection molding process may have a structure in which an EVOH layer is completely covered with another resin, for example a PES layer. Even though such moldings do not have an adhesive resin (Ad) layer between the EVOH layer and the PES layer, these multi-layered containers may have seemingly good appearance due to the adhesion affect of the ambient atmospheric pressure.
However, when such containers are filled with, for example, beverages, foods, etc., and experience a mechanical shock, for example by being dropped, the constituent PES layer(s) and EVOH layer(s) may readily delaminate, thereby seriously degrading the appearance of the container. This problem may be overcome by preparing coinjection molded containers having an Ad layer. Container structures such as PES/Ad/EVOH/Ad/PES (JP-A-56-501040) and PES/Ad/EVOH/Ad/PES/Ad/EVOH/Ad/PES (JP-A-50-135169, JP-A-61-152411, JP-A-61-152412, JP-A-61-259944) and the like have been investigated. However, the equipment for producing such structures is often extremely complicated, and controlling the thickness of each layer constituting the structure is often difficult. As a consequence, such containers are more expensive and more difficult to produce than multilayer containers having no Ad layer.
Other methods have also been investigated, in which EVOH is blended with other resins in order to increase the delamination resistance of containers which have no Ad layer. For example, JP-A-1-176554 discloses a method of blending EVOH with a polyamide-ester type thermoplastic resin. JP-A-1-182023 discloses a method of blending EVOH with a metal-containing polyester type thermoplastic resin. JP-A-3-175032 discloses a method of blending EVOH with a thermoplastic polyurethane. However, when EVOH is blended with such resins, containers with lower transparency are produced, which tend to have extremely poor appearance. In addition, the blending increases the production costs, and depending on the type of resins blended, the melt stability of the blends may be poor.
JP-A-3-175033 discloses a method of adding at least one salt selected from titanium salts, cobalt salts, manganese salts, antimony salts and germanium salts to EVOH in order to increase the delamination resistance of containers which have no Ad layer. However, the problem with this method is that the addition of such metal salts does not improve the delamination resistance of containers satisfactorily, and it also lowers the melt stability of EVOH.
JP-A-1-204736 discloses a method of blending a major EVOH component with a minor EVOH component in order to increase the delamination resistance of containers which have no Ad layer. The minor EVOH component has a larger ethylene content, a lower degree of saponification, a lower melting point and a larger melt index than the major EVOH component. However, containers produced by blending two different types of EVOH which have a 30 mol % or more difference in their ethylene content have low transparency and very bad appearance, as is shown in the examples of JP-A-1-204736. In addition, blending increases production costs, and the melt stability of the resulting blend may be poor.
The present invention provides multi-layered containers made by stretch-blow molding a preform which is prepared by coinjection-molding a polyester resin and an EVOH resin mixture. Even though containers formed by this method do not have an Ad layer, the containers have good impact delamination resistance and good gas-barrier properties. Other advantages of containers prepared by this method are that thay have high transparency, and stable resin melts.
The coinjection stretch-blow molded containers of the present invention comprise a thermoplastic polyester layer (layer A) and a resin composition layer (layer B) composed of a mixture of two EVOH copolymers (B1, B2), where layer A is in direct contact with both surfaces of layer B, and where the morphology of the resin composition is such that particles of EVOH B2 are dispersed in a matrix of EVOH B1, and the resin composition exhibits at least two crystal fusion peaks when analyzed by differential scanning calorimetry (DSC), and satisfies the following formulae (1) to (7):
60/40xe2x89xa6WB1/WB2xe2x89xa690/10xe2x80x83xe2x80x83(1)
25xe2x89xa6ETB1xe2x89xa640xe2x80x83xe2x80x83(2)
99xe2x89xa6SDB1xe2x80x83xe2x80x83(3)
35xe2x89xa6ETB2xe2x89xa648xe2x80x83xe2x80x83(4)
92xe2x89xa6SDB2xe2x89xa699xe2x80x83xe2x80x83(5)
8xe2x89xa6ETB2xe2x88x92ETB1xe2x89xa623xe2x80x83xe2x80x83(6)
1xe2x89xa6SDB1xe2x88x92SDB2xe2x89xa68xe2x80x83xe2x80x83(7)
where:
WB1 and WB2 are the amounts by weight of EVOH B1 and EVOH B2, respectively, in the resin composition, ETB1 and ETB2 are the ethylene contents (mol %), respectively, in EVOH B1 and EVOH B2, and SDB1 and SDB2 are the degrees of saponification (%), respectively, of EVOH B1 and EVOH B2.
Preferably, pellets of the resin composition are injection-molded, and the particles of EVOH B2 dispersed in the matrix of EVOH B1 in the starting resin composition have a mean particle size of at most 0.8 xcexcm.
Also preferably, the melt index of the two EVOHs (B1 and B2) satisfies the following formula (8):
0.1xe2x89xa6MIB1/MIB2xe2x89xa610xe2x80x83xe2x80x83(8)
where:
MIB1 and MIB2 are the melt indices of EVOH B1 and EVOH B2, respectively, measured in units of g/10 min, at 190xc2x0 C. under a load of 2160 g.
Preferably, the intrinsic viscosity IVA (dl/g) of the thermoplastic polyester satisfies the following formula (9) and the melt index of the resin composition (i.e., the blend of B1 and B2) MIB (g/10 min, at 190xc2x0 C. under a load of 2160 g) satisfies the following formula (10):
0.60xe2x89xa6IVAxe2x89xa60.90xe2x80x83xe2x80x83(9)
0.1xe2x89xa6MIBxe2x89xa610xe2x80x83xe2x80x83(10).
Preferably, the haze of the body of the container is at most 5%.
The container of the present invention may be used to hold essentially anything that may be filled into the container, for example, food, beverages, cosmetics, pharmaceuticals, etc. Preferably, the contents of the container of the present invention is a carbonated beverage, and the container has a capacity of at most 800 ml.
The present invention also relates to a preform for the container, the process of making the container, and the resin composition formed by blending B1 and B2.